PROJECT SUMMARY/ABSTRACT The disproportionate impact of the HIV/AIDS epidemic among U.S. Black gay, bisexual, and other men who have sex with men (GBMSM) is staggering. The epidemic is particularly dire for Black GBMSM who are young and live in the South. Black GBMSM between the ages 13 to 34 and those who live in the South accounted for 75% and 63% of HIV diagnoses among Black GBMSM in 2016, respectively. Most conceptualizations of intersectional stigma have been almost exclusively individualistic. Consequently, substantial gaps exist about how multilevel intersectional stigma ? individual (e.g., internalized HIV stigma, interpersonal discrimination), community (e.g., anti-gay stigma at church) and social-structural (e.g., criminal HIV exposure laws) ? interconnects to hinder HIV testing and PrEP use for young Black GBMSM in the South. There is also a dearth of validated measures of multilevel intersectional stigma available for HIV prevention research. To address these critical empirical gaps, a longitudinal exploratory-sequential mixed methods study (QUAL QUANT) is proposed to: (1) develop and validate self-report measures of individual, community, and social-structural-level intersectional stigma; (2) develop objective/non-self-report measures of social-structural stigma (e.g., based on Census data, laws, policies); and (3) produce visualizations of spatial stigma (e.g., living in and/or navigating impoverished and other stigmatizing places) for young Black GBMSM in two high HIV incidence southern cities: Washington, DC and Jackson, MS. Purposive sampling will be used to recruit 210 HIV-negative young Black GBMSM, ages 15 to 34. Phase I involves: (a) literature and policy reviews to identify existing measures of intersectional stigma and stigma-related laws and policies; (b) 60 in-depth individual interviews (30/city) to gain a rich and contextually-grounded understanding of multilevel intersectional stigma, and the use of maps to collect social and health activity space data relevant to spatial stigma; and (c) content validity assessments of the self-report measures by expert judges (n = 5 to 7) and Community Advisory Board (CAB) members (n = 24; 2 CABs/city). Phase II involves: (a) cognitive interviews with 20 participants (10/city) to refine the self-report measures; and (b) baseline and 6-month follow-up surveys of 130 participants (65/city) for psychometric analyses. Phase III involves the synthesis of the qualitative, spatial, and quantitative results and validity assessments of the synthesized results with CAB members in each city. The significance of the proposed research lies in the development of new multilevel intersectional stigma measures. The proposed research makes an innovative paradigmatic shift from the status quo with its theoretical and methodological fidelity to intersectionality?s core tenets. The expected outcome is the development of new self-report and objective/non- self-report measures of multilevel intersectional stigma that reflect the ?specific and particular? experiences of young Black GBMSM who live in two distinct southern cities. These measures will inform future HIV prevention research and interventions to improve the HIV prevention continuum for young Black GBMSM in the South.